In recent years, development for display panels such as cathode ray tubes, liquid crystal displays, and plasma display panels (hereinafter referred to as PDPs) has been aggressively pursued, as the demand for large-sized and high-definition display devices like hi-vision displays becomes increasingly larger.
Among various kinds of display panels, the PDPs are the most appropriate in order to make a thinner and larger display, and a 60-inch PDP has already been developed. AC surface discharge PDPs are the current main stream because this type is the most appropriate in order to make a thinner and larger display.
An AC PDP has such a structure that a front panel and a back panel face each other with barrier ribs therebetween, and a discharge gas mainly composed of a rare gas is enclosed in a discharge space between the two panels.
The front panel is such that scanning electrodes and sustaining electrodes are disposed in stripes on a main surface of a front substrate, and a dielectric layer made of lead-based glass and the like and a protecting layer made of MgO are layered in an order over the scanning and sustaining electrodes.
The back panel is such that data electrodes are disposed in stripes on a main surface of a back substrate, and a dielectric layer made of lead-based glass and the like is layered on the data electrodes. Further, plural lines of barrier ribs are disposed on the dielectric layer in parallel with the data electrodes, and phosphor layers, each being either red (R), green (G), or blue (B), are each disposed on walls of each gap enclosed by the dielectric layer and two adjacent barrier ribs.
In the AC PDP, each discharge cell corresponds to a part in the discharge space where the scanning and sustaining electrodes on the front panel and the data electrodes on the back panel cross with an overpass.
A plasma display device comprises the above described AC PDP and a driving circuit for driving the PDP.
In such a plasma display device, each discharge cell can only display two scales by either emitting light or not emitting light. Therefore, the AC plasma display device generally adopts an intra-field time division grayscale display method in order to display an image in grayscale. The intra-field time division grayscale display method is to display a grayscale image by dividing a field (16.6 msec) into plural subfields so as to divide light emission time into time slots. A field is a time unit for display.
Further, each subfield includes an initialization period, a write period, a discharge sustain period, and an erase period. An image is displayed by driving the PDP through each subfield including these periods.
However, the plasma display device having the above structure and adopting the above driving method is susceptible to charge errors where wall charge is not accumulated on surfaces of the phosphor layers or a surface of the protecting layer over the scanning electrodes, and instead, discharged out in the discharge space. This kind of charge errors in the write period leads to write errors and becomes one cause of deterioration of image qualities.
The above described write errors can be suppressed to an extent, by setting a write pulse voltage during the write period high. However, this is not a desirable solution because making the write pulse voltage high requires an IC having a high voltage resistance, or increases power consumption of an entire plasma display device.